Automotive vehicles are commonly equipped with dual-band personal communication systems (PCS) and digital/analog mobile phone service (AMPS) antennas. Such antennas have a height, for example, of at least 70 mm, and are implemented for cellular phone usage. Typically, these antennas are mounted exterior to the vehicle to achieve improved antenna performance and reduced radio frequency (RF) emissions to the inside of the vehicle. In many circumstances, height of the antenna may not be reduced because antenna performance may be compromised.
Due to high efficiency and ease of construction characteristics, helical wire antennas remain the first choice for many cellular antenna designers. For wire antennas, the optimum operation corresponds to λ/4 wavelength. The height, which is approximately 75-80 mm, is very close to λ/4 of the operation wavelength at the cellular phone lower frequency band (e.g. AMPS). This height may be further reduced using a normal-mode helical antenna. The height may be reduced to as little as 65 mm, however, a height reduction less than 65 mm may degrade the overall performance of the antenna.
Other known cellular antennas include a planar inverted circular/rectangular patch antenna having a reduced height, for example, of at least 30 mm. Additionally, the inverted path antenna has a higher linear gain. However, the diameter/width of antenna is undesirably increased to be at least 115 mm, and, are typically difficult to include dual band applications.
When antennas having large dimension width, but more often, height, are mounted on the exterior of the vehicle, the antenna becomes very noticeable, and often, unpleasant for vehicle users while introducing manufacturing difficulties for the OEMs. Accordingly, it is therefore desirable to provide an improved antenna assembly that is compact, provides adequate antenna performance, and offers multi-band capabilities.